High-Speed Downlink Packet Access (HSDPA) was introduced in Release 5 of the Third Generation Partnership Project (3GPP) standards for wideband code division multiple access (WCDMA) wireless communication networks. A key operating principle of HSDPA is to share a fast downlink (DL) pipe. An example of a fast DL pipe is a high-speed downlink physical shared channel (HS-DPSCH). A universal mobile telecommunication system (UMTS) Terrestrial Radio Access Network (UTRAN) may configure up to 15 HS-DPSCHs. Each HS-DPSCH may be shared by all wireless transmit/receive units (WTRUs) operating within the network on a per transmission time interval (TTI) basis, for example, every 2 millisecond. As a result, information on the downlink channels may be sent to a different WTRU in every 2 millisecond interval.
In order to allow WTRUs to determine ownership of the information on HS-DPSCH shared channels, a base station also sends one or more parallel high-speed shared control channels (HS-SCCHs). Among other things, the HS-SCCHs provide detailed data to enable receiving WTRUs to determine which information transmitted on the HS-DPSCH is addressed to a particular WTRU and to enable the particular WTRU to recover the transmitted information.
In HSDPA, a base station utilizes three key concepts to achieve high-speed data transmission. The three key concepts are: adaptive modulation and coding (AMC), retransmissions using a hybrid-automatic repeat request (HARQ), and base station scheduling.
A base station may take advantage of the changing channel conditions as perceived by a WTRU in communication with the base station. In order to accomplish this, the base station can schedule transmissions to maximize DL throughput, for example, using 16 quadrature amplitude modulation (QAM) for a WTRU close to the base station and using quadrature phase shift keying (QPSK) for a WTRU at cell edge. Such fast scheduling is complemented with the use of HARQs, allowing retransmission of transport blocks that are received at a WTRU with errors. The HARQs are implemented at a physical layer and multiple simultaneous HARQ processes are permitted in order to maximize utilization.
An ongoing problem in HSDPA compliant networks is latency within the UTRAN, especially in setup delays for packet switched (PS) and circuit switched (CS) calls. Reducing the delay during WTRU state transitions is one way to improve network performance.
As illustrated in FIG. 1, a WTRU compliant with current standards can be in one of 4 possible states when in a connected mode, CELL_DCH, CELL_FACH, URA_PCH, or CELL_PCH. The WTRU state is based on WTRU traffic volume and mobility. The WTRU may communicate with the UTRAN only when in Cell_FACH or Cell_DCH states. Cell_PCH and URA_PCH states are intended for power saving operation. URA_PCH is used by a highly mobile WTRU that changes cells frequently. In both of these power saving states, the WTRU has no uplink mechanism to send traffic to the UTRAN. However, the WTRU can be paged to notify it to change states to either a Cell_FACH state or Cell_DCH state.
The paging procedure is a two step process. To save battery power, a WTRU is configured with a discontinuous reception (DRX) cycle that shuts off the WTRU's receiver chain periodically. This is known as sleep mode. A WTRU is only awake (the receiver chain is on) for certain frames known as paging occasions. Within each paging occasion, a WTRU listens for a Paging Indicator on a Paging Indicator Channel (PICH). The Paging Indicator instructs a WTRU to monitor the paging channel (PCH) carried in the Secondary Common Control Physical Channel (S-CCPCH). The PCH is a transport channel that is mapped to a logical Paging Control Channel (PCCH).
Multiple S-CCPCHs may be used. The WTRU selects from among the multiple S-CCPCHs based on an Initial WTRU Identity. The selected S-CCPCH is associated with a single PICH. This is the PICH that the WTRU monitors for paging indications. There is a strict delay requirement between the PICH and the associated paging message on the S-CCPCH. This delay offset is defined to allow the WTRU to receive the PICH and then the paging message. 3GPP Release 6 specifies this offset as 7,680 chips, or 2 millisecond. After recovering the PCCH, the WTRU can either enter the Cell_FACH state and perform a CELL UPDATE or return to sleep mode until the next paging occasion.
One technique for reducing this state transition time is to map the PCCH to a high-speed downlink shared channel (HS-DSCH) instead of the PCH. A faster downlink rate results in a shorter transmission time for the paging message and faster state transitions. This protocol stack architecture is shown in FIG. 2. The inventors have recognized several problems that exist when mapping the PCCH to the HS-DSCH.
First, HSDPA is currently only allowed in the Cell_DCH state and is controlled by the WTRU variable HS-DSCH_RECEPTION.
Second, the HS-DSCH must be configured to operate in the downlink. This involves assigning a WTRU an address HS-DSCH Radio Network Temporary Identifier (H-RNTI), configuring a HS-SCCH channelization code, and configuring HARQ information, such as the number of HARQ processes and memory partition. Currently, there is no mechanism defined to allow such a configuration in Cell_PCH and URA_PCH states.
Third, a WTRU in Cell_PCH or URA_PCH state is unable to send channel quality indication (CQI) information to the UTRAN because no uplink communication is possible. Thus, the base station cannot take full advantage of the AMC techniques required by HSDPA.
Fourth, once a WTRU receives a Paging Indicator on the PICH, the WTRU expects a paging message in the associated S-CCPCH. This S-CCPCH occurs 7,680 chips after the PICH. In HSDPA, a base station schedules WTRU traffic. While it is possible to maintain a strict timing relationship between the PICH and the HS-DSCH, maintaining this relationship restricts the base station scheduling flexibility for transmission over HS-DSCH. Limiting the base station scheduling flexibility for HS-DSCH is undesirable since other types of traffic (for example, dedicated traffic channel (DTCH) and dedicated control channel (DCCH) are also carried over HS-DSCH.
Therefore, HSDPA paging of a WTRU in CELL_PCH and URA_PCH states without the above mentioned disadvantages is desired.